Clutch including a wear take-up device, in particular, for motor vehicles

ABSTRACT

A Friction clutch including a reaction plate (13, 16), a friction wheel 14 carrying on its outer periphery friction liners (30), a pressure plate (20), diaphragm (24), and a cover plate (17). One of the pressure (20) and reaction (13, 16) plates, includes two coaxial parts axially movably in relation to one another against a wear compensating mechanism (11). The clutch includes a rearming member (1) acted on by a locking member (2) controlled by a trigger (3). A first resilient spring (6) and loose coupling members (8, 80) operate between the rearming member 1 and a rotatable member (4) of the wear compensating mechanism (11). The rearming member (1) is acted on by a second spring (7).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a friction clutch, especially for amotor vehicle, and is directed more particularly to a mechanism forcompensating for wear in the friction liners, which operatescontinuously as the said liners become worn, and which thus ensures aclutch travel which remains constant over the course of time.

2. Description of the Prior Art

A conventional friction clutch includes a reaction plate, which may bein two parts so as to constitute a damped flywheel, and which is mountedin rotation on a first shaft, typically a driving shaft such as thecrankshaft of the internal combustion engine, and which carries at itsouter periphery a cover plate to which at least one pressure plate isattached.

The pressure plate is fixed to the cover plate and reaction plate, forrotation with them, but it is able to be displaced axially under thebiasing action of axially acting resilient means which are generallycontrolled by a metallic diaphragm which bears on the cover plate, whilea friction wheel which carries the friction liners at its outerperiphery, and which is fixed to a shaft, typically a driven shaft suchas the input shaft of the gearbox, for rotation with the latter, isinterposed between the pressure plate and the reaction plate in such away as to be gripped between them when the clutch is in its engagedposition.

The diaphragm controlling the axial movement of the pressure plate isactuated by a clutch release bearing which slides axially.

Over the working life of such a clutch, the friction liners, and alsothe materials against which they engage (i.e. the pressure plate and thereaction plate) become worn, which causes the gripping force between thefriction wheel on the one hand, and the pressure and reaction plates onthe other hand, to vary as a result of the modifications in the workingconditions of the diaphragm.

The clutch travel also varies, as does the force which necessary fordisengaging the clutch.

It is known from the document U.S. Pat. No. 4,207,972 to provide a wearcompensating device in which a first plate, which is in fact thepressure plate, is in two coaxial parts, one of which is displaceableaxially with respect to the other in such a way that the overallthickness of the first plate has a tendency to increase to the extentthat the thickness of the friction liners diminishes, so that theworking conditions of the diaphragm consequently do not vary.

In that document, the coaxial elements of the first plate aredisplaceable axially one with respect to the other against the action ofa device or mechanism for compensating for wear in the above mentionedfriction liners.

The said device includes ramp means which are carried in a complementarymanner by two members, one of the members being fixed against rotationwhile the other member is rotatable.

Initiation of the movement of the said members is controlled by atrigger which is responsive to the state of wear of the friction liners.The said members work between the two parts of the first plate.

Such a device enables wear in the friction liners to be taken upcontinuously.

However, under severe operating conditions, the pressure plate becomesheated, as do the remainder of the components of the clutch, so that asingular point is passed through with compensation for wear, thepressure plate becoming deformed into a conical shape.

An object of the present invention is to overcome this drawback.

SUMMARY OF THE INVENTION

According to the invention, a clutch of the type described above ischaracterised in that it includes a rotatable rearming member associatedwith one of the parts of the first plate and subjected to the action oflocking means which are controlled by the trigger, in that firstcircumferentially acting resilient means and loose coupling means areinterposed between the rearming member and the rotatable member of thewear compensating mechanism, and in that the rearming member issubjected to the action of second circumferentially acting resilientmeans working against the first resilient means and interposedoperatively between the rearming member and one of the parts of thefirst plate.

Thanks to the invention, the rearming member is armed while the clutchis in its engaged position with the liners worn, and wear is then takenup through a predetermined angle by the loose coupling means during thedisengagement of the clutch. With a diaphragm clutch, the accumulationof energy of the latter is made use of in arming the system, the clutchbeing engaged. Singular points are thus avoided, since the wearcompensating device works in a continuous manner through a predeterminedangle. The operation of taking up wear is initiated with the clutch inits engaged position.

The second resilient means are chosen in such a way as to overcome theaction of the first resilient means. Accordingly, they exert a highertorque on the rearming member, their force being for example greaterthan that of the first resilient means.

The wear compensating device is preferably disposed at the level of thereaction plate, the latter comprising two coaxial parts.

This wear compensating device is arranged at the inner periphery of thereaction plate proper, which offers a friction surface for engagement bythe friction wheel.

The wear compensating device is accordingly located in a relatively coolposition, and the clutch mechanism, and in particular the pressureplate, remains unchanged. In addition, the inertia of the arming memberis reduced, and good ventilation can be obtained.

In one embodiment, the locking means consist of a brake which preventsrotation of the rearming member.

In a modified version, locking may be obtained by mating cooperation.For example, the locking member may have lugs which cooperate with lugsformed in the arming member.

The locking means preferably include a resilient tongue which is actedon by the trigger.

In one embodiment, this trigger is mounted for sliding movement in thereaction plate proper, mentioned above, and is adapted to act on thetongue, being itself acted on by the pressure plate.

Thus, as the friction liners become worn, the pressure plate movescloser to the reaction plate proper, in such a way that at the end of acertain course of travel, it acts on the trigger, which in its turn actson the tongue of the locking means so as to release the latter.

The rearming member (the clutch being engaged) can then be displaced inrotation so as to arm the wear compensating device for movement throughan angle which is predetermined by the loose coupling means.

In a modified version, the wear compensating device is located at thelevel of the pressure plate.

In that case, the cover plate or the diaphragm is arranged to act on thetongue of the locking means in order to unlock the latter.

Preferably, the cover plate has an abutment lug for this purpose.

The following description illustrates the invention with reference tothe attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in axial cross section of a clutch having a wearcompensating device;

FIG. 2 is a view similar to FIG. 1 without the cover plate and part ofthe support plate of the reaction plate, and showing the trigger and thelocking means;

FIG. 3 is a partial view in perspective, showing the trigger, thelocking device, the arming member, and the wear compensating mechanismin accordance with the invention;

FIG. 4 is a view similar to FIG. 3, showing the normal state of the wearcompensating device after wear has been taken up;

FIG. 5 is a view similar to FIG. 4, showing the wear compensating devicein the state in which the clutch is engaged, after the friction linershave become worn, and after being armed;

FIG. 6 is a view similar to FIG. 5, showing the wear compensating devicein the declutched state, after the play has been taken up;

FIG. 7 is a diagrammatic view showing the location of the wearcompensating device of FIG. 1 at the level of the pressure plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a diaphragm clutch for a motor vehicle. This clutchincludes, in axial succession, a reaction plate in two parts 13, 16, aclutch friction wheel 14, a pressure plate 20, a diaphragm 24, and acover plate 17.

The reaction plate 13, 16 is arranged to be carried on a driving shaft,which in this example is the crankshaft 35 of the internal combustionengine, for rotation with the latter, while the friction wheel 14 iscoupled, either resiliently or rigidly, to a hub 28 which is carried onthe shaft 36 of the gearbox for rotation with the latter.

The friction disc 14 has at its outer periphery a support disc 29carrying friction liners 30 fixed on each of its faces.

The pressure plate 20 is fixed to the reaction plate 13, 16 and thecover plate 17, for rotation with these components.

More precisely, the assembly consisting of the pressure plate 20,diaphragm 24 and cover plate 17 constitutes a unitary assembly referredto as the clutch mechanism, which is carried, through the radial flangeof its cover plate 17 which is in the form of a hollow dish, on thereaction plate 13, 16.

In this example, the pressure plate 20 is coupled in rotation to thecover plate in a manner known per se, through interposed tangentialtongues 23 which are fixed at one of their ends to a zone of the radialflange of the cover plate, by means of fastening members (not shown),and which are fixed at their other ends to a projecting radial lug 22 ofthe pressure plate 20 by means of fastening members 12, which in thisexample are in the form of rivets.

The diaphragm 24, which in its relaxed state is of frusto-conical form,is mounted for pivoting movement on the cover plate 17.

More precisely, the diaphragm 24 includes a peripheral portion 39 in theform of a Belleville ring, together with a central portion which isdivided into radial fingers 40 by slots. These slots are open at one oftheir ends into the central aperture of the diaphragm, and at theirother end, at the inner periphery of the Belleville ring 39, into anenlarged aperture 41.

The base portion of the cover plate is press-formed with an asperity 25which constitutes a primary abutment for the diaphragm 24.

Fastening lugs 27, formed integrally by bending and press forming,project from the inner periphery of this base portion, with each of thelugs 27 extending axially through one of the above mentioned apertures41, and has at its free end a portion which is bent radially away fromthe axis of the assembly, so as to define a locating bend on which afrusto-conical crown ring 26 is mounted, the latter providing asecondary abutment aligned with the primary abutment 25.

More precisely, the outer peripheral portion of the Belleville ring 39of the diaphragm 24 bears on a divided projecting element 21 of thepressure plate 20, while at its inner periphery the Belleville ring 39is gripped between the primary abutment 25 and the secondary abutment26.

The clutch is normally engaged, and the friction liners 30 are clampedbetween the pressure plate 20 and the portion 16, described laterherein, of the reaction plate 13, 16. For this purpose, the diaphragm 24bears on the secondary abutment 25 and on the projecting element 21 ofthe plate 20, so as to bias the pressure plate 20 towards the reactionplate 16.

The friction liners are thus gripped between the pressure and reactionplates. When the liners 30 are new, the diaphragm 24 is generally flat(FIG. 1). In order to disengage the clutch it is necessary to act on theends of the fingers 40 of the diaphragm 24, with the aid of a clutchrelease bearing indicated diagrammatically at 37.

In a manner known per se, the clutch release bearing is subjected to theaction of a control member, such as a declutching fork or the piston ofan hydraulic actuator, and has an actuating element, which is typicallyin the form of a ball bearing, one of the rings of which is extended soas to make contact with the fingers 40 of the diaphragm.

The release bearing 37 is mounted for sliding movement along a guidetube 38 which is fixed to the casing of the gearbox (not shown) andwhich surrounds the input shaft 36 of the gearbox.

Thus, by exerting a thrust on the ends of the fingers 40 with the aid ofthe release bearing 37, the diaphragm is caused to deflect pivotally, sothat it then bears on its secondary abutment 25, the effect of which isto cancel the force exerted by the diaphragm on the pressure plate 20;the tongues 23 urge the plate 20 towards the base portion of the coverplate 17.

The friction liners 30 are thus released, and the clutch is disengaged.

In this example it will be noted that the cover plate 17 is fixed bymeans of the threaded fasteners 18 on the portion 13 of the reactionplate 13, 16 described later herein.

Thus, as the friction liners 30 become worn, the pressure plate 20 movescloser to the reaction plate 16, so that the inclination of thediaphragm 24, and therefore the force exerted by the said diaphragm 24on the plate 20, varies. The position of the release bearing 36 alsochanges.

In order to overcome this effect, a wear compensating device ormechanism 11 is provided, this being mounted within the clutch andworking in a continuous manner.

This wear compensating mechanism works between two coaxial parts whichare defined by a plate which is either the pressure plate or thereaction plate, and which is referred to for convenience as the firstplate.

This mechanism for compensating for wear in the above mentioned frictionliners 30 includes ramp means 90, 91. The two coaxial parts of the firstplate are coupled, through interposed coupling means, for rotationtogether, while one of them is movable axially with respect to theother.

Initiation of this movement of the said parts is controlled by a trigger3 which is responsive to the condition of wear of the friction liners30.

For this purpose, the mechanism 11 comprises two members 4, 5. One ofthese, 5, is fixed in rotation while the other one, 4, is rotatable.Each of these members carries complementary ramp means, for example ofthe helical type, which are associated with one of the parts of thefirst plate. The components of the compensator therefore work betweenthe two parts of the first plate.

More precisely, in accordance with the invention, a clutch having a wearcompensating mechanism of the type mentioned above is characterised inthat it includes a rotatable rearming member 1 which is associated withone of the parts of the first plate 13, 16 or 20, and which is acted onby locking means 2 which are controlled by the trigger 3, in thatcircumferentially acting first resilient means 6 and loose couplingmeans 8, 80 are operatively interposed between the rearming member 1 andthe rotatable member 4 of the wear compensating mechanism 11, and inthat the rearming member 1 is acted on by second circumferentiallyacting resilient means 7 which work against the first resilient means byoperating between the rearming member 1 and one of the parts, namely thepart 13, of the first plate 13, 16, 20.

The locking means 2 prevent the rearming member 1 from turning. They areso dimensioned as to resist both the force exerted by the spring 6, andthe inertia forces which are exerted on the rearming member 1.

The second means 7 are so chosen as to overcome the action of the firstmeans 6. They exert a greater torque on the rearming member. In thisexample the second resilient means have a force greater than that of thefirst resilient means, and work against the latter.

In this example (FIG. 1), the wear compensating means are interposedwithin the reaction plate 13, 16. The reaction plate comprises a supportplate 13 which carries at its outer periphery a starter crown 19, whichis arranged to be driven by the starter of the vehicle. It also includesa reaction plate 16 proper. The reaction plate 13, 16 thus comprises twocoaxial parts 13, 16, the plate 16 being movable axially with respect tothe support plate 13 in a manner to be described below.

This plate 13, which is of metal in this example, has at its outerperiphery an axially orientated cylindrical skirt portion 31, the freeend of which has a radial flange which extends away from the axis of theassembly.

It is on this flange that the cover plate 17 is fitted by means of thethreaded fasteners 18.

The support plate 13 is centered internally and fixed on the crankshaftby means of threaded studs 34, as can be seen in FIG. 1.

A centering member 33 is interposed between the heads of the studs 34and the corresponding face of the support plate 13.

This member 33 has at its outer periphery an axially orientated annularflange which centers the rotatable member 4 of the wear compensatingdevice.

The reaction plate 16 proper, which in this example is a casting, has afriction surface for engagement with the appropriate friction liner 30of the friction wheel 14.

The plate 16 is coupled in rotation to the support plate 13 throughtangential tongues 32, in the same way as the pressure plate 20 iscoupled to the cover plate 17.

To this end, the tangential tongues 32 are fixed at one of their ends tothe support plate 13 by means of fastening members,` and at their otherend to a radial lug of the plate 16, which in this example is a casting,by means of fastening members 15 which in this example are rivets.

The plate 16 is thus able to be displaced axially with respect to thereaction plate 13, while being coupled to the latter, for rotation withit, by means of the tongues 32. In this example there are several setsof tongues 32, which are spaced apart at regular intervalscircumferentially.

These tongues are preferably adapted to develop an axial force which issuch as to ensure the axial stacking of the assembly of the system.

In a modified version, a coupling of the tenon and mortice type could beprovided, with the skirt portion 31 then having longitudinal apertures,with a lug of the plate 16, constituting a tenon, being engaged in eachof these apertures.

In that case, a spring is preferably provided so as to ensure that thestack consisting of the components which constitute the compensator isheld together.

The plate 16 is extended at its inner periphery by an annular,transversely orientated, collar portion 160 which serves for fasteningone of the pieces, 5, of the mechanism 11 carried on the said collarportion. In a modified version, the member 5 may be integral with theplate 16, being formed by moulding with the latter.

It will be noted that the collar portion 160 is relieved locally so asto provide ventilation of the space which is defined by the supportplate 13 and the plate 16.

Profiles adapted to provide ventilation may also be provided between theplate 16 and the member 5.

The rearming member 1 is mounted in this space. The said member is thusinterposed between the plate 13 and the plate 16, being in contact withthe plate 13 and associated with the latter.

The said member 1 surrounds the rotatable member 4 of the device 11,centered by the member 33. More precisely, the members 4 and 5 are ofstepped, tubular form. The member 5 has a cross section in the form ofan inverted L, and has a tubular portion 92 of reduced diameter whichcarries a pin 96 for locating it in rotation on the collar portion 160.

The member 5 is preferably made of a synthetic material, as is themember 4.

The member 5 has a tubular portion 93 (FIG. 3) of enlarged diameter, thefront surface or edge of which includes part of the ramp means. Theseramp means consist in this example of at least two sectors 91 whichdefine helical ramps. In this example three sectors are provided. Thesaid member 5 is fixed in rotation to, but movable in straight linemovement with respect to, the plate 16, to which it is abutted and withwhich it is associated.

In a modified version not shown, the member 5 is integral with the plate16.

The member 4 has a tubular portion 94 of reduced diameter, the size ofwhich is complementary to that of the portion 93 of the member 5. Thefront edge or front face of the said portion 94 defines the other partof the ramp means, which in this example comprise three ramps 90, theprofile of which is complementary to the ramps 91. The tubular portion95, of enlarged diameter, of the said member 4 has notches 82, togetherwith a radial lug 8, at its outer periphery. The notches 82 have atruncated trapezoidal profile, with a flat base and two inclined sides.

The member 4 is fixed against axial movement, but is movable inrotation.

The disc-shaped rearming member 1 has at its inner periphery notches 81the profile of which is similar to that of the notches 82, but which areinclined in the opposite direction.

In this example there are three notches 81 and three notches 82, whichare spaced apart circumferentially on a circle and which are in facingrelationship with each other. Corrugated springs 6, with end portions inthe form of a dihedral, are mounted in the said notches 81, 82, whichdefine a corresponding dihedral at each of their circumferential ends.

These springs 6 constitute the first circumferentially acting resilientmeans in accordance with the invention.

The portion 95 of the member 4 has at its outer periphery a radiallyprojecting tooth 8 which penetrates, with a predeterminedcircumferential clearance, into a notch 80 formed at the outer peripheryof the rearming member 1.

This arrangement defines loose coupling means 8, 80 which areinterposed, in accordance with the invention, between the member 4,which will be referred to hereinafter as the adjusting ramp, and therearming member.

The said rearming member is acted on by second circumferentially actingresilient means 7, which in this example consists of a simple coilspring fixed at one of its ends to the member 1 and at its other end tothe support plate 13. This arming spring 7 is inclined in such a waythat it works in the circumferential direction.

It tends to cause the member 1 to rotate in a clockwise direction, andit exerts on the member 1 a force greater than that of the firstresilient means 6 which constitute resilient disengaging means.

The spring force of the resilient means 7 is greater than that of theresilient means 6. In particular, this result can be obtained byarranging that the stiffness of the spring 7 is greater than that of thesprings 6.

The member 1 is clamped at its outer periphery between the plate 13 anda member 2 in the form of an elastic brake. This member 2 is part of thelocking means in accordance with the invention, and includes at itsouter periphery a central declutching tongue 51, which is flanked by tworesilient fastening lugs 50, each of which is formed with a through holethrough which there passes a fastening member such as a rivet 52 (FIG.2), for fastening the brake 2 to the plate 13.

The inner periphery of the said member 2, which in this example is ofmetal, has a press-formed zone, which is rounded in this example, forgripping the member 1 in point contact. The said member 1 is thusclamped elastically between the plate 13 and the member 2.

It will be noted that the rearming member 1 is mounted for rotation onthe outer periphery of the member 4. The trigger 3 consists of a pinwhich is mounted so as to extend through an associated bore formed forthis purpose at the outer periphery of the plate 16 (FIG. 2).

In practice, a "mecanindus" pin (not shown) is interposed between theabove mentioned bore of the plate 16 and the pin 3, being such that thesaid pin 3 is mounted so that it is elastically gripped.

One of the ends of the pin is arranged to act on the tongue 51 of thebrake 2, while the other end of the pin 3 is arranged to make contactwith the rivet 12 by which the tongues 23 are fixed.

Thus, the head of the rivet 12, being fixed to the pressure plate 20, isadapted to interact with the pin 3.

The trigger is normally in contact with the tongue 51, and there is aclearance between the rivet 12 and the pin 3. The arming member is thuslocked.

When the friction liners 30 become worn, the pressure plate 20, andtherefore the rivet 12, come closer to the pin 3.

After wear has been taken up, or when the friction wheel is new, theconfiguration is as shown in FIG. 4, the clutch being engaged.

In this case, the spring 6 works in the clockwise direction, and the lug8 is abutted against one of the circumferential ends of the notch 80,there being an angle α (FIG. 4).

In this configuration, the member 1 is fixed because it is clamped bythe brake 2, in such a way that the spring 7 exerts no force on thespring 6, and the member 1 constitutes a fixed stop member for thesprings 6.

When the liners 30 become worn, the head of the rivet 12 acts on the pin3, which acts on the resilient tongue 51 and releases the brake in theclutch engaged position.

In that event, the rearming member 1 (FIG. 5) rotates in the clockwisedirection under the action of the spring 7, with the spring 6, having aweaker spring force, being compressed because the member 4 is then fixedsince the clutch is engaged.

In this way, the configuration of FIG. 5 is reached, in which the angleα is present between the other edge of the lug 8 and the other edge ofthe notch 80.

Thus rotation through a predetermined angle α has taken place while theclutch is engaged, with the members 4, 5 accordingly being immobile.

The wear compensating mechanism is thus armed, in a value which isdetermined in advance, the springs 6 being compressed.

When the clutch is disengaged, the distance between the plate 13 and theplate 16 can increase in such a way that the member 4 rotates through anangle α (FIG. 6).

In this connection, in that position the rearming member is fixed, beingonce again gripped by the brake 2 because the pressure plate is spacedaway from the pin 3, which enables displacement to occur only through anangle α.

The member 4, referred to as the adjusting member, thus rotates throughan angle α from its FIG. 5 position, and the springs 6 are expanded.

Thus, thanks to the invention, a limited rotation takes place betweenthe members 4 and 5.

It will be noted that these members 4, 5 are only able to rotate in onedirection, because of the angle of friction of the ramps 90, 91, whichis chosen with this in view.

Thus, under severe operating conditions of the clutch, wear will only betaken up through an angle α. In this way, all singular points, and allpoints of excessive compensation, are avoided.

The low inertia of the rearming member, fitted under precompression,will be noted. Its inertia has no influence on the rearming operation,because of the springs 6, 7 which are loaded accordingly.

It is of course possible to fit the wear compensating device at thelevel of the pressure plate 20 (FIG. 7).

The latter accordingly has on its rear face a ramp portion 5, the end ofwhich defines ramp means as in FIG. 1. This member is therefore fixedagainst rotation but movable in the axial direction.

The member 4 is enabled to make contact with the member 5, and also hasramp means, which in this example are of the helical type like those ofthe member 4.

In this example, a member 120 is mounted in rotation on the plate 20,being movable axially with respect to the latter. The member 120 has forthis purpose an axially oriented portion which slides in grooves formedin an internal bore of the plate 5.

To this end, the member 120 is in the form of a comb at its free end,such that a splined coupling is formed between the plate 20 and themember 120 which is centered by the plate 20. The said member providesan abutment for the diaphragm 24, and is extended at its outer peripheryso as to carry the brake 2. The rearming member is then clamped at itsouter periphery between a transverse portion of the member 120 and thebrake 2.

The rearming member is mounted for rotation on the member 4 as in FIGS.1 to 6, with springs 6 and 7, not shown, being interposed.

It will be noted that the member 120 centers the member 4 and carriesthe members 1, 4, 6, 7, 2.

In this example the trigger is constituted by a lug 3 which projectsfrom the cover plate and which is formed by press forming and bending.

As the liners become worn, the plate 20 is displaced closer to the lug3, and the brake 2 then comes into abutment, through its resilienttongue, against the lug 3, which releases the brake 2.

In a modified version, the trigger could be constituted by thediaphragm. In that case, the brake 2 includes an axial portion which isarranged to cooperate with the diaphragm.

The device operates then in the same way as that in FIG. 1.

It will however be appreciated that the wear compensating device of FIG.1 does not call for any modification of the clutch mechanism 20, 24, 17,and that it is located in a less hot position. In addition, the inertiaof the rearming member 1 is reduced, which has the least possible effecton operation.

By contrast, the device 11 in FIG. 7 is located in a hotter position.

The present invention is of course not limited to the embodimentdescribed. In particular, the clutch may be of the pull-to-release type,with the diaphragm then bearing on the cover plate through the outerportion of its Belleville ring, and bearing through the inner peripheryof its Belleville ring on the projecting element of the pressure plate.In this case it is necessary to work in traction on one end of thefingers of the diaphragm in order to release the clutch.

In a modified version, instead of a diaphragm it is possible to make useof axially acting resilient means in the form of coil springs acting onthe base portion 17 of the pressure plate 20, and any type of mechanicaland/or hydraulic gripping means may also be employed.

These springs are then acted on by declutching levers.

It will be noted that the rearming member 1 further includes, at itsouter periphery, a lug 9 which enables the initial position of themember 1 to be set, for example with the aid of a tool such as ascrewdriver.

The structures can of course be reversed, with the rearming member thenhaving a lug mounted with a clearance in a notch of the member 4.

The rearming member 1 preferably defines wear indicating means.

The springs 6 and 7 may be coil springs or springs of rubber or asynthetic material, mounted in windows.

It will be noted that the spring 7 constitutes an arming spring, andthat the spring 6 constitutes a release spring.

In a modified version, the arming member 1 may have axial lugs whichpenetrate with a predetermined clearance into apertures in the adjustingmember 4, so as to define the loose coupling means.

In another modified version, the ramp means are defined by the diaphragm24 which, for this purpose, has a corrugated configuration.

In a further modified version, the ramp means are formed between thediaphragm and the cover plate.

It will be appreciated that as the liners 30 become worn, the force ofthe diaphragm 24 increases in such a way that this increase in energy ismade use of in order to arm the system.

I claim:
 1. A friction clutch comprising; a reaction plate (13, 16) forrotation with a driving shaft, a friction wheel (14) which is adaptedfor rotation with said driving shaft and which carries friction liners(30) at its outer periphery, a pressure plate (20), axially actingresilient means (24), a cover plate (17) which is fastened on thereaction plate (13, 16), rotational coupling means (23) operativelyinterposed between the pressure plate (20) and an assembly consisting ofthe cover plate (7) and the reaction plate (13, 16), for coupling thepressure plate (20) to said assembly for rotation with, and for axialmobility with respect to the latter, wherein one of the platesconsisting of the pressure plate (20) and the reaction plate (13, 16),referred to as the first plate, comprises two coaxial parts (13, 16; 20,120), one of which is displaceable axially with respect to the otheragainst the action of a wear compensating mechanism (11) interposedbetween said parts and comprising ramp means working between two members(4, 5), each of which is associated with a respective one of the saidparts of the first plate (20; 13, 16), one of the latter being rotatablewhile the other is fixed against rotation, and a trigger (3) responsiveto the state of wear of the friction liners (30), for controlling theinitiation of movement of said parts of the first plate (13, 16),wherein said clutch includes a rotatable rearming member (1) associatedwith one of the parts of the first plate (13, 16; 20) and subjected tothe action of locking means (2) which are controlled by the trigger (3),first circumferentially acting resilient means (6) and loose couplingmeans (8, 80) are interposed between the rearming member (1) and therotatable member (4) of the wear compensating mechanism (11), therearming member (1) is subjected to the action of secondcircumferentially acting resilient means (7) working against the firstresilient means (6) and interposed operatively between the rearmingmember (1) and one of the parts of the first plate (13, 16; 20), andsaid second resilient means (7) exert on the rearming member (1) atorque which is greater than that exerted by the said first resilientmeans (6).
 2. A clutch according to claim 1, wherein the locking meanscomprise a brake (2).
 3. A clutch according to claim 2, wherein thelocking means (2) are fastened on one of the parts of the first plate(13, 16), and have a resilient tongue (51) which is subjected to theaction of the trigger (3).
 4. A clutch according to claim 3, wherein thelocking means (2) have a profiled portion for clamping the rearmingmember (1) between the latter and said part of the first plate.
 5. Aclutch according to claim 1, wherein the rearming member (1) is mountedfor rotation on the rotatable member (4) of the wear compensating device(11).
 6. A clutch according to claim 5, wherein the rearming member (1)surrounds said movable member (4) of the wear compensating mechanism. 7.A clutch according to claim 6, wherein the rearming member (1) has aninternal notch (80) into which there penetrates, with a circumferentialclearance, a lug (8) of the rotatable member (4) of the wearcompensating device (11).
 8. A clutch according to claim 1, wherein thefirst circumferentially acting resilient means (6) are mounted innotches (81, 82) formed in facing relationship with each other in therearming member (1) and in the rotatable member (4) of the wearcompensating mechanism (11), respectively.
 9. A clutch according toclaim 1, wherein the second resilient means (7) consist of an inclinedcoil spring which is anchored in the rearming member (1) and in theappropriate part (13, 120) of the first plate.
 10. A clutch according toclaim 1, wherein the reaction plate (13, 16) is in two parts, and inthat the rearming member (1) and the wear compensating device (11) actbetween the two parts (13, 16) of the said reaction plate.
 11. A clutchaccording to claim 10, wherein one of the parts consists of a supportplate (13) while the other one of the parts 20 consists of a plate (16)constituting the reaction plate and having a friction surface to theappropriate friction liner (30).
 12. A clutch according to claim 11,wherein the rearming member (1) is clamped between the support plate(13) and the locking means (2).
 13. A clutch according to claim 12,wherein the reaction plate proper (16) has at its inner periphery acollar portion (160) for fixedly mounting the member of the wearcompensating mechanism (11) that is fixed against rotation.
 14. A clutchaccording to claim 13, wherein the components of the wear compensatingmechanism (11) are centered by a member which is fixed on the supportplate (13).
 15. A clutch according to claim 9, wherein the pressureplate (20) is in two parts, and in that the rearming member (1) and thewear compensating device (11) work between the two parts 15, 120) ofsaid pressure plate.